This invention relates generally to color display and reproduction systems and, more particularly, to a graphical and interactive user interface for user control of the mapping of a palette of colors from one device gamut to another on such systems.
Increasingly affordable and available computer controlled color display and reproduction systems will promote wider use of color in document-intensive industries or document-intensive functional areas of enterprises. Using color effectively in environments that support diverse color systems to produce color display and printed materials requires reducing the complexity of color specification so that the occasional as well as the expert color user may select, modify, and apply color aesthetically and appropriately for its intended use.
Some color specification systems utilize a device dependent color classification model which provide color descriptor classifications that are derived from, and which control, associated physical devices. Such device dependent color classification models include the additive red, green, and blue (RGB) phosphor color model used to physically generate colors on a color monitor, and the subtractive cyan, magenta, and yellow, plus black (CYMK) color model used to put colored inks or toners on paper. These models are not generally correlated to a human color perceptual model. This means that these device dependent color models provide color spaces that treat color differences and changes in incremental steps along color characteristics which are useful to control the physical devices but which are not validly related to how humans visually perceive or describe color. Furthermore, considerable trial and error may be required to select a specific color or to achieve a desired color modification because the color model and its color space representation is not uniform to the user, and a large change in one or more of the physical descriptors of the color space, such as in the R, G, or B dimensions, will not necessarily result in a correspondingly large change in the perceived color.
Other color models exist which are geometric representations of color, based on the human perceptual attributes of hue, saturation, and value (or brightness or lightness) dimensions (HSV). While providing some improvement over the physically based RGB and CMYK color models, these color specifications are conveniently formulated geometric representations within the existing physically based color models, and are not psychophysically validated perceptually uniform color models.
The nonuniformity of the underlying color model directly impacts the effectiveness of a color selection and editing user interface. A color selection and editing user interface provides the control and communications link between the system user and the underlying color model. The interface provides a color space in which the user selects and edits colors. A color space is a pictorial or graphical representation or construction of a color model, visually showing the mathematical representations of colors. User interfaces based on conventional nonuniform color models generally limit user editing functions to selecting colors from fixed palettes of colors or to providing a mechanism by which the user may create and modify colors by specifying percentages of certain primary colors, either via text input, or by manipulating graphical tools such as sliding color bars, or color wheels.
Color selection user interfaces using nonuniform color models are those typically provided with personal computer business graphics software. One such representative color selection tool is provided with PowerPoint.TM. software from Microsoft Corporation of Redmond, Washington. PowerPoint.TM. is software for planning, composing, and creating presentations. The User's Manual for the software designed for use on certain Apple.RTM. Macintosh.TM. computers discloses at pp. 326-340 a window-based user interface with a menu for selecting the presentation's color scheme. A color scheme dialog box allows the user to select a presentation color scheme from preset color schemes of eight colors. To add colors to the color scheme or modify an existing color, the user selects colors from a color chart of eighty eight colors, or from a color wheel by dragging a cursor around the wheel until the desired color appears in a rectangular box in the dialog window.
Brief descriptions of several types of color models and color selection tools are also provided in Stone, M., "Color, Graphic Design, and Computer Systems", Color Research and Application, Vol. 11 (Supplement), pp. S75-S82, 1986 (hereafter, "Stone, `Color, Graphic Design, and Computer Systems`"). Additional computer controlled color editing systems are disclosed in Guitard and Ware, "A Color Sequence Editor", ACM Transactions on Graphics, 9:3 (July 1990), at pp. 338-341; in Bergstedt, U.S. Pat. No. 4,694,286, entitled "Apparatus and Method for Modifying Displayed Color Images", and in Holier, U.S. Pat. No. 4,721,951, entitled, "Method and Apparatus for Color Selection and Production".
In particular, Bergstedt discloses, in U.S. Pat. No. 4,694,286, an apparatus and method which permit selection of colors for display, and modification of displayed colors. A color index is associated with each pixel of a displayed image. Upon positioning of a cursor at a pixel of a displayed image, the user may modify the hue, lightness, and saturation of the color associated with the color index of that pixel location, thus modifying all pixels in the image having the color associated with the color index. Modification is accomplished by successive actuation of hue, lightness, and saturation keys on a keyboard input device, in accordance with a hue, lightness, and saturation color cone shown in FIG. 5 therein.
Holier discloses, in U.S. Pat. No. 4,721,951, an apparatus and method wherein a color is selected in the basis of one color characteristic system for implementation in another color characteristic system. Color selection is made from the color characteristic system of hue, saturation and value (referenced as brightness) (HSV) in the preferred embodiment, and is performed interactively with the operator individually selecting hue, saturation and brightness levels from displays which illustrate the effects of changing each of these characteristics. The displays are comprised of a display bar for each of the hue, saturation and brightness color characteristics, with the selected value or level for each characteristic being shown by a vertical black line, or slide marker, which the operator may move to a selected position. The selected values of H, S, and V are converted through the use of appropriate transforms to values of R,G, and B in the red, green, and blue color classification system for display in the current color display.
A uniform color space, based on an underlying uniform color model, attempts to represent colors for the user in a way that corresponds to human perceptual color attributes that have been actually measured. Using a device independent and uniform color model as a basis for specifying and manipulating color provides a foundation for more user control, accuracy, and precision in color selection and editing, since color specification is not tied to the physical characteristics of a particular color rendering device. One such device independent color specification system is that developed by the international color standards group, the Commission Internationale de I'Eclairage (the "CIE"). CIE color specification employs device independent "tristimulus values" to specify colors and to establish device independent color models by assigning to each color a set of three numeric tristimulus values according to its color appearance under a standard source of illumination as viewed by a standard observer. Each set of X, Y, and Z tristimulus values represents a color according to its spectral power distribution, as a summation of the color contributions of all wavelengths within the spectral distribution of a color sample, corrected for the light source used to illuminate the colored sample and for the color sensitivity of the standard observer. The CIE has recommended the use of two approximately uniform color spaces for specifying color: the CIE 1976 (L*u*v*) or the CIELUV color space, and the CIE 1976 (L*a*b*) color space (hereafter referred to as "CIELAB" space or "LAB" space).
Some color display and reproduction systems utilize uniform color models. Taylor et. al., in EP 0 313 796 A3, entitled, "Computer display color control and selection system", disclose an interface system for use in selecting and controlling colors in graphics images generated by a computer system. The interface comprises a mechanism and method for displaying a graphical representation of hue, chroma and lightness combinations available based on a color appearance type color space and associated mechanism. The interface provides for a graphical representation which includes a graph of the range of hues in one dimension and a second graph of the range of chroma and value combinations in two dimensions. The preferred embodiment of the interface makes use of a specially defined HVC color space for graphically displaying, representing, and selecting hue, chroma and value combinations for a color with a high degree of perceptual uniformity. The preferred embodiment of the system includes a mechanism for operating the interface in three different modes, providing functions corresponding to picture editing, color map editing, and continuous shading. Picture editing allows an individual color in a graphics image to be edited by positioning a cursor on a pixel in the image associated with the color to select the color for editing. Color map editing allows the color data corresponding to various parts of a graphics image to be directly manipulated. Continuous shading allows a range of colors to be generated between two colors specified by the user for smooth shading applications.
Robertson, P. K., in "Visualizing Color Gamuts: A User Interface for the Effective Use of Perceptual Color Spaces in Data Displays", IEEE Computer Graphics & Applications, September, 1988, pp. 50-64, discloses the use of uniform color spaces in computer graphics and image processing applications. Robertson discloses interactively controlled representations of the perceptual color gamuts of color display devices, and how these representations may be of value in color specification and data display. In particular, two-dimensional cross-sectional representations of these gamuts can be used to indicate available colors on a display device and for guiding the choice of color for representing data. Various forms of gamut representations are illustrated, including a leaf structure schematic of a three dimensional gamut of a color monitor, two dimensional cross sections through the CIELUV gamut of a color monitor and CIELAB gamut of a film or print recording device, cross sections of constant lightness through the film or print CIELAB gamut, and superimposed cross sections of constant lightness through the CIELUV gamut of a color monitor and the film or print CIELAB gamut.
An interactive palette selection system is disclosed in Hedin, C. and Derefeldt, G., "Palette--A Color Selection Aid for VDU Images", Perceiving, Measuring, and Using Color: Proceedings of SPIE, Vol. 1250, Santa Clara, Calif., Feb. 15-16, 1990, pp. 165-176. A color database of a predetermined number of colors, specified in RGB and tristimulus values, is colorimetrically measured from a color monitor under standard viewing conditions. The database also specifies each color in CIELUV L*, u*, and v* coordinates, chroma (C*.sub.uv) and hue (h.sub.uv) coordinates, and NCS (Natural Color System) notations. A palette of colors can be created from the color database from predefined searches of the color database according to certain restrictions. The palette is displayed around the border of a display screen. The palette can be plotted in various color diagrams such as the NCS hue triangle, and the CIELAB a*-b* plane. The palette can be reduced and sorted, and colors can be selected from the palette and used to change or adjust a portion of a displayed image.
Stone, in "Color, Graphic Design, and Computer Systems", at pgs. S78-79, discloses a tool for color selection in calibrated systems which allows a user to explore a color space model based on X, Y, and Z tristimulus values, mapped into the 1931 Chromaticity Diagram, in the context of a particular device such as a color monitor. The monitor's gamut is defined as a triangle in the x, y plane and only the region inside the triangle is active, automatically constraining the values of x and y. Luminance is controlled separately.
Bauersfield and Slater, in "User-Oriented Color Interface Design: Direct Manipulation of Color in Context", 1991, at pg. 418, column 1, and Bauersfield and Price, in "The 3 D Perceptual Picker: Color Section in 3 D", 1990, at page 182, first and second columns, disclose a color selection tool called the 3 D Perceptual Picker which uses a three-dimensional visualization based on the Munsell color model for color selection. Bauersfield and Price disclose a color space window containing one "page" of the color model presented to the user for color selection. The user may directly manipulate the model to locate and select colors, with the selected color appearing in a second, selection window. Bauersfield and Slater disclose, at pg. 418 column 1, in the last full paragraph, a color swatch interface device in the same tool for color selection tasks. The sizable and form-adjustable color swatch allows the user to move a shape of the desired color to any location on the screen.
An additional issue in the successful use of color is controlling the color appearance of colors when they are translated from one color reproduction device to another. For purposes of this discussion, a color's appearance will include its color attributes, such as, for example, hue, chroma, and lightness. Device independent color specification facilitates color reproduction among diverse color devices. A device "gamut" includes all of the colors physically producible from the primary colors on a particular device, and may be defined in a device independent form. Different color reproduction devices have different gamuts, and thus, there is no one-to-one color correspondence between device gamuts. The device independent color specification for a color on one device may then be mapped to the same device independent color specification for the corresponding color within the gamut of another device. In devices having automated color correction processes, this mapping generally assumes that the goal of color correction is to produce what is called a "metameric" match between colors.
There are, however, many variables influencing color appearance not taken into account by automated color correction and metameric matching. Preserving certain relationships between colors and achieving consistent and appropriate colors in a document or image may be far more important to the user than a producing metamerically matching colors. In addition, color correction between color systems employing different device dependent models may introduce color appearance errors, depending on the type of automatic correction algorithm used. Automatic correction algorithms, then, which are beyond the control of the color user, may affect the information content or visual effect being conveyed in the document, illustration, drawing, or graph. These color reproduction issues are more completely described by Hansen in "Breaking the Color Barrier", Computer Graphics World, July, 1990, pg. 39-48, incorporated herein by reference. Users who want to incorporate color effectively in printed materials need the ability to directly and predictably control color appearance across different color devices, by being able to precisely and easily modify colors on one device for predictable reproduction on another device.
Alessi et. al., U.S. Pat. No. 4,958,220, discloses a color image reproduction apparatus in which an operator may preview on a video monitor, before printing, a reproduced, scanned color image as it would appear on any of a variety of image receptive output media, such as reversal film, or negative film to print material, or reversal film to print material. Each scanned input image is first transformed, via an appropriate look up table from a first set of lookup tables, to a device independent database color space, and from the device independent database color space, via an appropriate look up table from another set of lookup tables, to a selected hard copy representation. The computer-based workstation includes operator control apparatus which enables an operator to interact with the workstation to provide input information, image manipulation commands pertinent to modifying the image displayed, and output information. Image manipulation commands include the ability to independently control color quantities of hue, chroma, and lightness.
The prior art color selection or editing systems previously described which are not based on uniform color models either provide fixed palettes of color for selection, or require a nonintuitive, often unpredictable, approach to achieving a desired color modification because changes in one or more of the physical descriptors of the color space, such as in the R, G, or B dimension, do not necessarily result in a corresponding change in the perceived color. Other prior art color selection or editing systems which are based on uniform color models may be narrowly tailored for specific color selection purposes, such as scientific mapping or adjusting colors for photographic film reproduction, do not provide for complete manual control over color mapping between display and print device gamuts, only provide for single color editing, or do not provide the user with both direct image pixel manipulation and color palette manipulation. In addition, many of the previously described color selection tools do not display an entire palette of colors at one time so that a user may immediately perceive and preserve color relationships among all colors when one color is changed.
What is needed, therefore, is a system and method for color selection and color modification which provides visually intuitive and directly manipulable ways of organizing, managing, and predicting color in the context of a uniform color model. The graphical user interface of the present invention displays an entire palette of colors in a two dimensional view of a uniform color space while permitting the user to edit individual palette colors by directly manipulating the colors in the color space. Thus, the graphical user interface makes explicit to users the relationship among colors in the palette of colors as they are being edited. In addition, the present invention provides a facility for the user to manually control how a color will be reproduced in a given device gamut, on one or more output devices. The graphical user interface also provides support for various user skill levels so that both the experienced graphical artist or designer, trained in the principles of using color effectively and familiar with using the uniform color spaces, as well as the casual user, who may only create or use color illustrations or color documents occasionally, may utilize their respective skill levels to benefit from an easy and intuitive access to the full range of colors available on the devices being used.